Re: How to manually add a new interface to a bridge device?

[Zoltan Frombach <zoltan@xxxxxxxxxxxx>]

BTW, adding a 2nd virtual nic to a guest can also be done with command line tools (I just googled this for you) :
https://kashyapc.fedorapeople.org/virt/add-network-card-in-guest.txt
( It came up as 1st result when I searched for: virsh add network interface to existing guest )

But if you look at the bottom of this guide, they also mention that if something goes wrong, they resort to using virsh edit just like I suggested to you. See, I prefer to edit a configuration file rather then issuing long and complicated commands on the CLI. However, being able to add a 2nd nic to a live guest is nice though and that could only be achieved with the CLI command. As you can see, you can even add nic's to a VM without having to reboot it.

Zoltan

On 12/9/2015 10:58 AM, Howard Leadmon wrote:

How do you decide what MAC address to use for that VM interface?   As I just tried to change the MAC to some other value close, like I made '52:54:00:34:e1:21' into say '52:54:00:34:e1:32', and when I try and load it in, I get the following:

 

error: XML error: Attempted double use of PCI Address '0:0:4.0'

 

 

Here is one of my network entries:

 

    <interface type='bridge'>

      <mac address='52:54:00:34:e1:21'/>

      <source bridge='br1'/>

      <model type='virtio'/>

      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>

    </interface>

 

 

---

Howard

 

From: centos-virt-bounces@xxxxxxxxxx [mailto:centos-virt-bounces@xxxxxxxxxx] On Behalf Of Zoltan Frombach
Sent: Wednesday, December 9, 2015 4:24 AM
To: Discussion about the virtualization on CentOS <centos-virt@xxxxxxxxxx>
Subject: Re: How to manually add a new interface to a bridge device?

 

You most definitely do not need to destroy and re-create a VM just to add a 2nd network interface.

I don't think those vnet interfaces got created by the host OS. I believe those are created by KVM (or libvirt) when you start a VM. I could be wrong though. But I just checked on my CentOS 6 KVM host machine and I see as many vnet interfaces as many VMs are currently running (or if one VM has two virtual network cards then of course that VM results two vnet interfaces shown on the host). Here the relevant part from one such VM's XML file (those XML files are under the /etc/libvirt/qemu directory on my CentOS host ) :

    <interface type='bridge'>
      <mac address='00:16:36:e2:20:ea'/>
      <source bridge='br0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <interface type='bridge'>
      <mac address='00:16:36:e2:20:eb'/>
      <source bridge='br600'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </interface>

As you can see, there are two interfaces defined in this VM's XML file. One is connected to the host's br0 interface and the 2nd is connected to the host's br600 interface. You must make sure that all your mac addesses are unique on your network though!!

After editing a VM's XML file with your favorite editor, you need to execute this command:
virsh define /etc/libvirt/qemu/your-vm-name.xml
or just simply use this editor:
virsh edit your-vm-name
(but I hate vi, so I use my favorite editor and when I finished editing I just run virsh define.)

I edited VM's XML files many times and I can add/remove virtual network cards without problems.

Zoltan

On 12/9/2015 9:55 AM, Howard Leadmon wrote:

Tried that as well, but this has to be something that gets set at the OS level and loaded, as if you look at dmesg output, you can see all the vnet?? nodes as the OS comes online.    So the question is, what is virt-install doing that creates the needed vnet interface that is part of the bridge.   I really had to kill and reload the VM just to load a second interface..

 

 

---

Howard Leadmon

 

From: centos-virt-bounces@xxxxxxxxxx [mailto:centos-virt-bounces@xxxxxxxxxx] On Behalf Of Zoltan Frombach
Sent: Wednesday, December 9, 2015 2:42 AM
To: Discussion about the virtualization on CentOS <centos-virt@xxxxxxxxxx>
Subject: Re: How to manually add a new interface to a bridge device?

 

I would stop the VM, edit its definition file (that's an XML file) and then start it up. But be careful: After you edit the XML file, you need to execute a command so KVM re-reads that file. I forgot that command, but you can look it up on Google.

On Dec 9, 2015 7:52 AM, "Howard Leadmon" <howard@xxxxxxxxxxx> wrote:

 

Maybe my google-fu is failing me, but I have spent the past couple hours looking at how to add a vnet? Device to my KVM host running CentOS 6, and for the life of me I can’t get this going.   

 

From all my research if I want to add a device I should just do ‘brctl addif br1 vnet14’ if I want to add a vnet14 to bridge br1.   When I do this, I get:

 

# brctl addif br0 vnet14

interface vnet14 does not exist!

 

 

If I run a ‘brctl show’ I get the following:

 

# brctl show

bridge name     bridge id               STP enabled     interfaces

br0             8000.00237dd22a4c       no              eth0

                                                        vnet0

                                                        vnet10

                                                        vnet11

                                                        vnet13

                                                        vnet2

                                                       vnet3

                                                        vnet4

                                                        vnet6

                                                        vnet8

br1             8000.00237dd22a50       no              eth1

                                                        vnet1

                                                        vnet12

                                                        vnet5

                                                        vnet7

                                                        vnet9

 

 

Needless to say the existing vnet?? Devices are in use on guest VM’s currently.

 

When I create a new VM using virt-install, I usually add the following to my command line:

 

--network=bridge:br0 --network=bridge:br1

 

I messed up building a new VM, and only added the br0 interface to the VM, but need the br1 interface as well.  So my question is, or a pointer to how I can add that br1 interface to my existing VM, and create the needed vnet14 interface for it to attach to?

 

If anyone can explain how to do this, or give me a good pointer on where the info is on how to do this, it would sure be a huge help..

 

Thanks…

 

 

---

Howard Leadmon

 

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